Or a personal principle or set of principles to live by? Some sort of conclusion or mantra you've came up with over the years or have come to believe, dictating the way you live your life and perceive the world.

For myself, I try to consciously embrace the moment-to-moment nature of life. Not think of it in explicit stages of progress (school, graduation, work, marriage, etc), if you get what I mean. I consider the future always, but I live for the moment. Secondly, I think that everything is significant in some way. I am very averse to writing something off as being unimportant or insignificant, and am very careful to say something like "Who cares?".

Screw other people.
I'm always right.
Everyone else's opinions are wrong unless it is agreeing with my superior opinion.
Using "IMO" as a defense is wrong.

I think I lost track of things there.

I try to live....free. Free of hate or anger, to simply flow like a river, for this moment has already passed.

I do my best to adhere to what you might call Ahimsa although it's not religious I just think good begets good. I believe in morals without the need for religious justification.

I'm the exact opposite of that. Most of what I do is with the future in mind, and I think this is my "philosophy" on life - that our purpose is to further humanity and make the future better.

That's not to say that I don't enjoy the present, of course.